Yes, Texas Instruments does that, I had the same experience (were we involved in the same project?). They do it if they are strategically interested in a certain market segment. Your project might look like a demo to them — worth investing some time and effort into.

Unfortunately, I'd say they are the exception. Good luck even getting someone at Broadcom or Qualcomm to speak to you. If your projected volumes are not (convincingly) into at least hundreds of thousands, you will get a simple "no", if you even manage to get an answer at all.